An important parameter that determines whether styrene-butadiene rubber can be used in the manufacture of tires and other elastomeric commercial products is the rubber's compatibility with commonly used fillers, such as carbon black and silica. An increase in the interactions between styrene-butadiene rubber and inorganic filler can be achieved by introducing appropriate functional group-containing polymeric fragments that enhance the polymer's affinity to the applied filler.
U.S. Pat. No. 4,935,471 B discloses that the introduction of nitrogen-containing functional groups into the polymer structure results in a strong enhancement of the affinity of functionalized polymers to carbon black. A clear increase in the compatibility of modified polybutadiene with the filler was observed even after the introduction of one terminal functional group containing a tertiary nitrogen atom (e.g. —CN or —NMe2) into polymer chains. In addition to the increase in affinity of the modified polymer to the filler, a clear improvement in filler dispersion in the rubber compound was observed. In the examples of U.S. Pat. No. 4,935,471, methods for the synthesis of initiators of living anionic polymerization based on aromatic N-heterocyclic compounds such as pyrrole, imidazole, pyrazole, pyrazine, pyrimidine, pyridazine, and phenanthroline derivatives and their use in the production of N-functionalized polybutadienes are described. A similar approach is disclosed in U.S. Pat. No. 6,515,087 B, EP 0 590 491 A1 and WO2011/076377 A, where acyclic and cyclic amines are employed for the preparation of active initiators for anionic polymerization. In a further step, amines are used for the preparation of di-N-functionalized styrene-butadiene polymers.
Silicon and/or nitrogen atom-containing vinyl compounds are further taught in US 2004/0044202 A1, EP 2 749 575 A1, US 2012/0041134 A1, EP 2 277 940 A1, and US 2004/0063884 A1.
The synthesis of di-N-functionalized styrene-butadiene polymers is also disclosed in U.S. Pat. Nos. 4,196,154 B, 4,861,742 B and 3,109,871 B. However, to obtain the above polymers, amino-functional aryl methyl ketones are applied as reagents. The latter plays also the role of a functionalizing agent and polymerization terminating agent. The above N-modification methods only allow the preparation of polydienes containing no more than two amino-functional groups per polymer chain.
Another approach to prepare N-functionalized polymers with different N-functional group contents consists in the introduction of suitable styrene monomers into the polymer chain. The controlled introduction of the styrene monomers to the reaction system will result in a wide range of styrene-butadiene rubbers with different N-functional group contents, thereby with different dispersion properties for inorganic fillers. US2007/0123631 A1 discloses the preparation of N-functionalized styrene monomers via the reaction of a diverse range of acyclic and cyclic lithium amides (LiNR1R2, e.g. LiNEt2, LiNMePh, LiN(SiMe3)2, LiNC4H8, and LiNC5H10) with 1,3- or 1,4-divinylobenzene, 1,3-di(isopropylene)benzene or a mixture of isomeric chloromethylstyrenes that in a further step are used in the preparation of styrene-butadiene rubbers with different contents of amino-functional groups.
EP 2 772 515 A1 teaches a conjugated diene polymer obtained by polymerizing a monomer component including a conjugated diene component and a silicon-containing vinyl compound. The silicon-containing vinyl compound may be a silyl-substituted styrene. However, the compounds according to EP 2 772 515 A1 are hydrolytically unstable under the typical processing conditions, compare the N,N-bis(SiMe3)2 aniline derivatives disclosed in Organic Letters 2001, 3, 2729.
The prior art is only concerned with the preparation of N-functionalized polydienes with a different content of N-functionality which can interact with commonly-used fillers, i.e. silica and carbon black through non-covalent interactions. However, standard formulations very often comprise both types of filler, silica and carbon black, in different ratios.
Therefore, it was the object of the present invention to overcome the disadvantages associated with the prior art and to provide functionalized styrene derivatives whose application in the synthesis of polydienes leads to in-chain modified SBR polymer compositions that have better affinity to both of the two typical fillers commonly applied in tire production, i.e. silica and carbon black. The functionalized styrene derivatives should also be hydrolytically more stable than those of EP 2 772 515 A1.